Free-standing diamond structures and methods

ABSTRACT

The present invention is directed in one aspect to methods of making free-standing, internally-supported, three-dimensional objects having an outer surface comprising a plurality of intersecting facets wherein a sub-set of the intersecting facets have a diamond layer of substantially uniform thickness. The diamond layer may be formed by chemical vapor deposition (CVD) over the surface of a substrate that has been fabricated to form a mold defining the sub-set of intersecting facets. A backing layer may be formed over at least a portion of the exposed diamond layer to enhance the rigidity of the layer when the substrate is removed.

CLAIM OF PRIORITY

This application claims the benefit of the filing date priority of U.S.Provisional Application No. 60/445,237 filed Feb. 6, 2003; No.60/494,089 filed Aug. 12, 2003; and No. 60/494,095 filed Aug. 12, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to free-standing objects having laboratorygrown diamond surfaces and methods for fabricating such objects. Moreparticularly, the present invention is directed to such objects andmethods wherein the outer surface of the object includes a plurality ofintersecting facets having a diamond layer.

Diamond is one of the most technologically and scientifically valuablematerials found in nature due to its combination of high resistance tothermal shock, extreme hardness, excellent infrared transparency, andexcellent semiconductor properties.

Diamond has the highest known isotropic thermal conductivity and arelatively low expansion coefficient thus providing it with desirableresistance to thermal shock. Because of these properties, diamond hasfound increasing use as a thermal management material in electronicpackaging of devices such as high power laser diodes, multichip modules,and other microelectronic devices.

Diamond is also the hardest known material and has desirable resistanceto abrasion. Thus diamond components and coatings have found increasinguse as wear resistance elements in various mechanical devices and incutting and grinding tools. Diamond is also highly resistant tocorrosion.

Diamond is also a good electrical insulator, but can be synthesized tobe electrically conducting by the addition of certain elements such asboron to the growth atmosphere. Diamond is also used in manysemiconductor devices including high-power transistors, resistors,capacitors, FET's, and integrated circuits.

The scarcity and high cost of natural diamond has prohibited itswidespread commercial use. However, the development of various methodsfor synthesizing diamond has made the widespread commercial use ofdiamond possible. The most commercially promising method forsynthesizing diamond includes the growth of diamond by chemical vapordeposition (CVD).

Diamond synthesis by CVD has become a well established art. It is knownthat diamond coatings on various objects may be synthesized, as well asfree-standing objects. Typically, the free-standing objects have beenfabricated by deposition of diamond on planar substrates or substrateshaving relatively simple cavities formed therein. For example, U.S. Pat.No. 6,132,278 discloses forming solid generally pyramidal or conicaldiamond microchip emitters by plasma enhanced CVD by growing diamond tofill cavities formed in the silicon substrate. However, there remains aneed for methods of making free-standing, internally-supported,three-dimensional objects having an outer surface comprising a pluralityof intersecting facets (planar or non-planar), wherein at least asub-set of the intersecting facets have a diamond layer.

Accordingly, it is an object of the present invention to obviate many ofthe deficiencies in the prior art and to provide novel methods of makingfree-standing structures having diamond surfaces.

It is another object of the present invention to provide novel methodsof making structures using diamond CVD.

It is yet another object of the present invention to provide novelstructures formed by diamond CVD.

It is still another object of the present invention to provide novelmethods of making free-standing structures having an exposed diamondsurface.

It is a further object of the present invention to provide novel methodsof making internally-supported structures having an exposed diamondsurface.

These and many other objects and advantages of the present inventionwill be readily apparent to one skilled in the art to which theinvention pertains from a perusal of the claims, the appended drawings,and the following detailed description of the preferred embodiments.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing the steps of the preferred embodimentof the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In one aspect, the present invention is directed to methods of makingfree-standing, internally-supported, three-dimensional objects having adiamond layer on at least a portion of the outer surface of the object.The diamond layer may be formed by any method of synthesizing diamondsuch as high-pressure, high-temperature (HPHT) methods or CVD. Inaccordance with the preferred embodiment of the present invention, thediamond is synthesized by CVD.

In the diamond CVD methods according to the present invention, a mixtureof hydrogen and carbon-containing gases is activated to obtain a regionof gas-phase non-equilibrium adjacent the substrate on which the diamondwill be grown. The carbon-containing gas may be selected from a largevariety of gases including methane, aliphatic and aromatic hydrocarbons,alcohols, ketones, amines, esters, carbon monoxide, carbon dioxide, andhalogens. Methane is used according to the preferred embodiment of theinvention.

The mixture of gases is energized to obtain a region of gas-phasenon-equilibrium adjacent the substrate on which the diamond will begrown. A variety of gas-phase activation techniques may be used andthese techniques may be categorized as either hot-filament CVD,plasma-assisted CVD, or flame CVD. In plasma-assisted CVD the plasma maybe generated by a number of energy sources including microwave,radio-frequency, or direct current electric fields.

The substrate may be any material suitable for nucleating and growingdiamond such as semiconductor, metal, and insulator materials.Generally, the nucleation rates are much higher on carbide formingsubstrates (e.g., Si, Mo, and W) than on substrates that do not formcarbides. According to the preferred embodiment of the presentinvention, silicon substrates are used in view of the desirablenucleation rates and well known fabrication techniques of silicon.

The surface of the substrate on which the diamond will be grown may bepretreated by various techniques to enhance diamond nucleation andimprove the nucleation density of diamond on the surface. Such methodsmay include (i) scratching, abrading, or blasting the surface withdiamond particles or paste, (ii) seeding the surface with submicronpowders such as diamond, silicon, or cBN, (iii) biasing the substrate,(iv) carburization, (v) pulsed laser irradiation, and (vi) ionimplantation.

In accordance with the preferred embodiment of the present invention, afree-standing, internally-supported, three-dimensional object isprovided having an outer surface comprising a plurality of intersectingfacets wherein at least a sub-set of the intersecting facets have adiamond layer of substantially uniform depth. The term “facet” as usedherein, includes a surface or face that is either planar or non-planar.

FIG. 1 illustrates the various steps of the preferred embodiment of thepresent invention. With reference to FIG. 1, a silicon substrate 10 isfabricated using conventional fabrication techniques to form a moldhaving an exposed surface 12 defining the sub-set of intersectingfacets. A diamond layer 14 of generally uniform thickness is grown overthe exposed surface 12 of the substrate 10 by any suitable method suchas hot-filament CVD or plasma-assisted CVD.

The exposed surface 12 may be pretreated by any suitable technique toenhance the diamond nucleation and nucleation density on the exposedsurface. Typically, the exposed surface is pretreated by seeding thesurface with carbon atoms 16. The pretreatment of the exposed surfacemay be important in order to ensure growth of the diamond in the shapeof the sub-set of facets which may be relatively complex.

In some instances, a backing layer 18 may be formed over at leastportions of the exposed surface of the newly grown diamond layer toprovide structural support to the diamond layer when the substrate isremoved. Any material that will adhere to the exposed diamond andenhance the rigidity of the diamond layer 14 is suitable for the backinglayer 18 (e.g., epoxy, plastic, viscous polymers that harden, glass,etc.). The backing layer may be electrically conductive ornon-conductive as desired.

Once the backing layer 18 is formed as desired, the substrate 10 isremoved to expose the surface 20 of the diamond layer 14 growncontiguous to the substrate which has been defined by the mold formed bythe substrate. The substrate 10 may be removed by any suitable meanssuch as chemical etching. The diamond layer 14 may then be treated asdesired.

The free-standing objects made according to the present invention mayfind utility in a variety of applications such as backward waveoscillators, bi-polar plates for fuel cells, traveling wave tubes,microchannel plates, and a multitude of other devices having a surfacecomprising a plurality of intersecting facets wherein a sub-set ofintersecting facets have a diamond layer of substantially uniformthickness.

While preferred embodiments of the present invention have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the invention is to be definedsolely by the appended claims when accorded a full range of equivalence,many variations and modifications naturally occurring to those of skillin the art from a perusal hereof.

1-34. (canceled)
 35. A free-standing, internally-supported,three-dimensional object having an outer surface comprising a pluralityof intersecting facets, at least a sub-set of said intersecting facetshaving a diamond layer of substantially uniform depth.
 36. Thethree-dimensional object of claim 35 further comprising a backing layer.37. The three-dimensional object of claim 35 wherein said sub-set ofintersecting facets includes planar facets.
 38. The three-dimensionalobject of claim 35 wherein said sub-set of intersecting facets includesnon-planar facets.
 39. A free-standing, internally-supported,three-dimensional object comprising a rigid backing layer, said objecthaving an outer surface comprising a plurality of intersecting facets,at least a sub-set of said intersecting facets having an exposed diamondsurface.
 40. The three-dimensional object of claim 39 wherein saidbacking layer is electrically conducting.
 41. The three-dimensionalobject of claim 39 wherein said backing layer is electricallynon-conducting.
 42. The three-dimensional object of claim 39 whereinsaid backing layer is an epoxy.
 43. The three-dimensional object ofclaim 39 wherein said sub-set of intersecting facets include planarfacets.
 44. The three-dimensional object of claim 39 wherein saidsub-set of intersecting facets include non-planar facets.
 45. Anapparatus comprising: a rigid backing layer; and a diamond structure ofsubstantially uniform depth overlaying at least a portion of saidbacking layer, said diamond structure having an exposed surface forminga plurality of intersecting facts.
 46. The apparatus of claim 45 whereinsaid exposed surface is suitable for guiding high frequency radiation.47. The apparatus of claim 45 having a size and shape suitable forforming a bi-polar plate for a fuel cell.